Enzymes which are able to degrade cellulose have previously been suggested for the conversion of biomass into liquid fuel, gas and feed protein. However, the production of fermentable sugars from biomass by means of cellulolytic enzymes is not yet able to compete economically with, for instance, the production of glucose from starch by means of .alpha.-amylase due to the inefficiency of the currently used cellulolytic enzymes. Cellulolytic enzymes may furthemore be used in the brewing industry for the degradation of .beta.-glucans, in the baking industry for improving the properties of flour, in paper pulp processing for removing the non-crystalline parts of cellulose, thus increasing the proportion of crystalline cellulose in the pulp, and in animal feed for improving the digestibility of glucans. A further important use of cellulolytic enzymes is for textile treatment, e.g. for reducing the harshness of cotton-containing fabrics (cf., for instance, GB 1 368 599 or U.S. Pat. No. 4,435,307), for soil removal and colour clarification of fabrics (cf., for instance, EP 220 016) or for providing a localized variation in colour to give the fabrics a "stonewashed" appearance (cf., for instance, EP 307 564 ).
The practical exploitation of cellulolytic enzymes has, to some extent, been set back by the nature of the known cellulase preparations which are often complex mixtures of a variety of single cellulase components, and which may have a rather low specific activity. It is difficult to optimise the production of single components in multiple enzyme systems and thus to implement industrial cost-effective production of cellulolytic enzymes, and their actual use has been hampered by difficulties arising from the need to employ rather large quantities of the enzymes to achieve the desired effect.
The drawbacks of previously suggested cellulolytic enzymes may be remedied by using single-component enzymes selected for a high specific activity.
Single-component cellulolytic enzymes have been isolated from, e.g. Trichoderma reesei (cf. Teeri et al., Gene 51, 1987, pp. 43-52; P. M. Abuja, Biochem. Biophys. Res. Comm. 156, 1988, pp. 180-185; and P. J. Kraulis, Biochemistry 28, 1989, pp. 7241-7257). The T. reesei cellulases have been found to be composed of a terminal A region responsible for binding to cellulose, a B region linking the A region to the core of the enzyme, and a core containing the catalytically active domain. The A region of different T. reesei cellulases has been found to be highly conserved, and a strong homology has also been observed with a cellulase produced by Phanerochaete chrysosporium (Sims et al., Gene 74, 1988, pp. 411-422).